Converted my Frankenstein Model III to use 3.5" floppies

[Chromedome45]

I know a lot of you have done this and I also did it to my Model 4. But Now it's the Model III's turn. Used Samsung 1.44 drives and a fully pinned home made cable. Works great and can get 720k storage on each drive. If anyone decides to do this make sure one of the drives can be converted to use DS0. A lot of modern drives don't support this anymore. I know the TEAC FD-235HF can and that' what is being used in the Model 4. For either it may be desoldering a very small solder pad and apllying solder to the DS0 pad. One small side effect the computer is a little lighter! On a side note if anyone decides to do this you can use 1.44 floppies just make sure to cover the density select hole. Otherwise get verify errors after formattting.

Pics:

 

[amadama]

Wow, that's really impressive. Congratulations!
Where can I find some information on doing this?

 

[Al Hartman]

3.5" drives also use less power than the full height 5.2" drives and so, stress the power supply less.

 

[jltursan]

And 3.5" floppies are by far, easier to dump than the nitpicking 5.25" ones!. IMHO this is the best mod you can do to a Model III/IV machine. Someday, if I can get a 128K PAL IC or substitute, I'll convert it into the perfect CP/M machine

Where can I find some information on doing this?

In fact it's extremely simple. Use a straight Floppy cable with no mods at all and connect to 3.5" drives than can be modded to be DS0 or DS1 at will. Obviously, if you want to boot with it, it'll need to be DS0. I've found that some brands may be troublesome, don't know why; try always a couple of different 3.5" drives.

As I've left as DS1 the old Tandon unit, I needed to replace the original shunt in the drive with a dipswitch and select the drive manually to be DS1.

 

[Al Hartman]

Why some drives may be problematic is probably due to the termination of signals in the drive. Terminating resistors used to be optional, and like SCSI... only on the last drive in the chain. At some point, it was decided to put termination at the disk controller and smaller terminating resistors in the drives. With only two drives on the cable, and the cable being short... this worked.

But, because the TRS-80 was designed prio to this, some drives which have incorrect termination for the controller used, might give you problems.

At least, that's what I think the problem is.

 

[Unknown_K]

Are you going to find some black faceplates for the drives (or maybe paint them silver)?

 

[Al Hartman]

Are you going to find some black faceplates for the drives (or maybe paint them silver)?

I've collected some black faced drives in case I decide to do the same thing.

 

[leeb]

When I put the 3.5 in my 4p I rewired the cable to allow 'normal PC' floppies to work 'as is' (except for the HD sensor which I disabled)...

Looks like this:




Should work just fine on a 3 as well! :D

 

[Chromedome45]

I kind of like the contrast of the white drives to the black background. But I will eventually put in some black ones as time permits.